During her final illness, St. Thérèse of Lisieux, the 19th-century French Carmelite nun who is now widely revered as “The Little Flower,” faced a similar trial, which seemed to center on doubts about whether anything awaited her after death. “If you only knew what darkness I am plunged into,” she said to the sisters in her convent. But Mother Teresa’s “dark night” was of a different magnitude, lasting for decades. It is almost unparalleled in the lives of the saints.

In time, with the aid of the priest who acted as her spiritual director, Mother Teresa concluded that these painful experiences could help her identify not only with the abandonment that Jesus Christ felt during the crucifixion, but also with the abandonment that the poor faced daily. In this way she hoped to enter, in her words, the “dark holes” of the lives of the people with whom she worked. Paradoxically, then, Mother Teresa’s doubt may have contributed to the efficacy of one of the more notable faith-based initiatives of the last century.

Few of us, even the most devout believers, are willing to leave everything behind to serve the poor. Consequently, Mother Teresa’s work can seem far removed from our daily lives. Yet in its relentless and even obsessive questioning, her life intersects with that of the modern atheist and agnostic. “If I ever become a saint,” she wrote, “I will surely be one of ‘darkness.’ ”

Mother Teresa’s ministry with the poor won her the Nobel Prize and the admiration of a believing world. Her ministry to a doubting modern world may have just begun.